threads = []
1.times do |i|
  threads << Thread.new do
    b = Benchmark.measure do
      code.call
    end
    puts b
  end
end
threads.each {|t| t.join }

yields

1.470000   0.220000   1.690000 (  1.894148)


threads = []
5.times do |i|
  threads << Thread.new do
    b = Benchmark.measure do
      code.call
    end
    puts b
  end
end
threads.each {|t| t.join }

yields

1.830000   0.270000   2.100000 (  5.176225)
  9.690000   1.240000  10.930000 ( 17.328003)
  9.730000   1.250000  10.980000 ( 17.394973)
 10.090000   1.270000  11.360000 ( 18.084461)
 10.150000   1.290000  11.440000 ( 18.221553)